The prior art is aware that in the conditioning of natural and synthetic gases to remove the acid gases such as hydrogen sulfide, carbon dioxide, carbonyl sulfide and the like, other acids, such as formic, sulfuric sulfurous, thiocyanic, oxalic, chloric acids as well as other acids, are generally also present in these gases and these acids form heat stable salts with the amine sorbents. These salts build up in the amine treating solution and must periodically be removed to maintain the overall efficiency of the amine with respect to regeneration for reuse in the absorbing process. The conventional manner for renewal of an amine sorbing solution contaminated with the heat stable salts, of the aforestated acids, is to transport the amine solution to a caustic treater wherein the salts are decomposed to their respective amine and acid components, wherein the latter is recovered as the alkali salt of the acid. Such processes are time consuming, not readily adaptable to field unit operations on site of the absorber and are relatively expensive, particularly because of the need to transport the solution to be regenerated from the site to a caustic processing plant which to be economically viable must serve several absorber operations.
It has been known for considerable time that amine salts in general and those produced as a result of the gas conditioning of natural and synthetic gases could be regenerated by electrochemical action. For example, Shapiro, U.S. Pat. No. 2,768,945, teaches one method for separating acidic gases from aqueous alkanolamine solutions used as absorbing solutions in the gas conditioning field. The Shapiro technique uses an electrochemical treatment of a portion of the thermally regenerated sorbing solution, a side stream, in a cell which separates the anode and cathode compartments from each other by use of a porous diaphragm. The anode is graphite and the cathode is steel. The anolyte is a weak acid and the catholyte is the amine solution. In another patent, Kuo et al, U.S. Pat. No. 3,554,691, the electrolytic conversion of amine salts of the principal acid gases, such as hydrogen sulfide and carbon dioxide, is described without mention of the effect of such electrochemical conversion of the other heat stable salts, viz., the amine formates, thiocyanates, sulfates, sulfites, oxalates, chlorides and the like. This patent uses a multi-compartment cell having at least one ion exchange resin-water compartment separating the electrode compartments each from intermediate compartments, which intermediate compartments include an acid compartment and product compartment, respectively, and a central feed compartment, all defined by ion (cation or anion exchange) permeable membranes between compartments.
Neither of these processes is known to be used today, Shapiro being comparatively more expensive to operate than periodic purging of a portion of the sorbent and replenishment with virgin sorbent diluting the heat stable salt concentration to a level whereat the effect of the presence of the tied up (protonated) amine is minimized. Kuo et al is far too expensive to operate since a multiplicity of cells between electrodes increases the internal resistance of the cell increasing operating costs at least proportionally.